Back side metallization

ABSTRACT

An integrated circuit device wafer includes a silicon wafer substrate and a back side metallization structure. The back side metallization structure includes a first adhesion layer on the back side of the substrate, a first metal later over the first adhesion layer, a second metal layer over the first metal layer, and a second adhesion layer over the second metal layer. The first includes at least one of: silicon nitride and silicon dioxide. The first metal layer includes titanium. The second metal layer includes nickel. The second adhesion layer includes at least one of: silver, gold, and tin.

RELATED APPLICATIONS

This application is a divisional application of U.S. application Ser.No. 15/669,361, filed on Aug. 4, 2017, having inventors Thomas P.Dolbear et al., titled “BACK SIDE METALLIZATION”, which is owned byinstant Assignee and is incorporated herein by reference.

BACKGROUND OF THE DISCLOSURE

The disclosure relates to semiconductor devices and the manufacturing ofsemiconductor devices. More specifically, the disclosure relates toimproved back side metallization for integrated circuit device wafersand die.

Integrated circuits are used in computing devices such as, but notlimited to, smart phones, tablets, wearables, laptops, desktops,internet servers, printers, and other devices. Integrated circuits canhave very dense circuitry and can operate at very high frequencies toprovide ever-improving levels of performance. Some devices may havemultiple processor cores and/or very large memory arrays on relativelysmall die. In operation, such devices can produce heat in excess of 100watts. If the heat is allowed to build up on the die, the performance ofthe integrated circuit may be degraded and/or the life of the integratedcircuit may be significantly shortened.

In some integrated circuits, a thermally conductive layer is applied tothe back side of the die and bonded to a heat sink, such a package lid.The package lid can have larger area than the back side of the die andmay be exposed to a convective flow of air to remove heat from thepackage lid. The thermally conductive layer can provide a thermal paththrough which the heat may flow from the die to the package lid todissipate from the package lid.

The flow of heat through the heat path can be significantly reduced ifthe bond between the thermally conductive layer and the back side of thedie fails. Thus, good adhesion between the back side of the die and thethermally conductive layer is an important factor in removing the heatbuild-up and consequently, in the reliability of the integrated circuitdevice.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure will be more readily understood in view of the followingdescription when accompanied by the below figures and wherein likereference numerals represent like elements, wherein:

FIG. 1 is a schematic top view of a multi-chip package, according tosome embodiments of the disclosure.

FIG. 2 is a schematic side cross-sectional view of the multi-chip moduleof FIG. 1, according to some embodiments of the disclosure.

FIG. 3 is a schematic side cross-sectional view of an integrated circuitdevice wafer, according to some embodiments of the disclosure.

FIG. 4 is a magnified schematic side cross-sectional view of a portionof the multi-chip module of FIG. 2, according to some embodiments of thedisclosure.

FIG. 5 is a magnified schematic side cross-sectional view of a portionof the integrated circuit device wafer of FIG. 4, according to someembodiments of the disclosure

FIG. 6 is a magnified schematic side cross-sectional view of a portionof the integrated circuit device wafer of FIG. 4, according to someother embodiments of the disclosure.

FIG. 7 is a flowchart illustrating a method for forming a metallizationstructure on a back side of a silicon wafer substrate, according to someembodiments of the disclosure.

FIG. 8 is a flow chart illustrating a method for forming a metallizationstructure on a back side of a silicon wafer substrate, according to someother embodiments of the disclosure.

FIG. 9 is a flowchart illustrating a method for making an apparatusincluding a package substrate, a lid attached to the package substrate,and a plurality of integrated circuit die from an integrated circuitdevice wafer, according to some embodiments of the disclosure.

FIG. 10 is a magnified schematic side cross-sectional view of a portionof the integrated circuit device wafer of FIG. 4, according to someother embodiments of the disclosure.

FIG. 11 is a flowchart illustrating a method for making an apparatusincluding a package substrate, a lid attached to the package substrate,and a plurality of integrated circuit die from an integrated circuitdevice wafer including forming a metallization structure on a back sideof the integrated circuit device wafer, according to some otherembodiments of the disclosure.

DETAILED DESCRIPTION OF EMBODIMENTS

Embodiments of the disclosure include back side metallization structuresthat can provide good adhesion between a back side of an integratedcircuit die and a thermally conductive layer to enable reliabledissipation of heat from the integrated circuit during operation. In oneexample, an integrated circuit device wafer includes a silicon wafersubstrate and a back side metallization structure. The silicon wafersubstrate has a front side surface and a back side surface opposite thefront side surface. The silicon wafer substrate includes a plurality ofintegrated circuits on front side surface. The back side metallizationstructure on the back side surface includes a first adhesion layer, afirst metal layer, a second metal layer, and a second adhesion layer.The first adhesion layer is on the back side surface. The first adhesionlayer includes at least one of: silicon nitride and silicon dioxide. Thefirst metal layer is over the first adhesion layer. The first metallayer includes titanium. The second metal layer is over the first metallayer. The second metal layer includes nickel and, optionally, vanadium.The second adhesion layer is over the second metal layer. The secondadhesion layer includes at least one of: silver, gold, and tin.

In one example, the device wafer further includes a plurality of solderbumps on the front side surface of the wafer substrate, the solder bumpselectrically connected to the plurality of integrated circuits. In oneexample, the first adhesion layer has a thickness from 100 nanometers to400 nanometers. In one example, the first adhesion layer consists ofsilicon nitride. In one example, the second adhesion layer is silver. Inanother example, the second adhesion layer consists of tin. In yetanother example, the second adhesion layer consists of gold. In oneexample, each of the plurality of integrated circuits includes centralprocessing unit cores.

In another example, an integrated circuit device wafer includes asilicon wafer substrate and a back side metallization structure. Thesilicon wafer substrate has a front side surface and a back side surfaceopposite the front side surface. The silicon wafer substrate includes aplurality of integrated circuits on front side surface. The back sidemetallization structure on the back side surface includes a firstadhesion layer, a first metal layer, a second metal layer, and a secondadhesion layer. The first adhesion layer is on the back side surface.The first adhesion layer includes aluminum. The first metal layer isover the first adhesion layer. The first metal layer includes titanium.The second metal layer is over the first metal layer. The second metallayer includes nickel and, optionally, vanadium. The second adhesionlayer is over the second metal layer. The second adhesion layer includesat least one of: silver and tin.

In one example, the device wafer further includes a plurality of solderbumps on the front side surface of the wafer substrate, the solder bumpselectrically connected to the plurality of integrated circuits. In oneexample, the first adhesion layer has a thickness from 100 nanometers to400 nanometers. In one example, the second adhesion layer consists ofsilver. In another example, the second adhesion layer consists of tin.In one example, each of the plurality of integrated circuits includescentral processing unit cores.

In one example, a method of forming a metallization structure on a backside of a silicon wafer substrate includes forming a first adhesionlayer on the back side of the silicon wafer substrate, forming a firstbarrier layer including titanium metal over the first adhesion layer,forming a second barrier layer including nickel and, optionally,vanadium over the first barrier layer; and forming a second adhesionlayer over the second barrier layer. The silicon wafer substrateincludes a plurality of integrated circuits formed on a front side ofthe silicon wafer substrate. The first adhesion layer includes at leastone of: silicon dioxide and silicon nitride. The second adhesion layerincludes at least one of: silver, gold, and tin.

In one example, the first adhesion layer is formed by chemical vapordeposition. In one example, the first adhesion layer has a thicknessfrom 100 nanometers to 400 nanometers. In one example, the firstadhesion layer consists of silicon nitride. In one example, the secondadhesion layer consists of silver. In another example, the secondadhesion layer consists of tin.

In one example, a method of forming a metallization structure on a backside of a silicon wafer substrate includes forming a first adhesionlayer on the back side of the silicon wafer substrate, forming a firstbarrier layer including aluminum over the first adhesion layer, forminga second barrier layer including nickel and, optionally, vanadium overthe first barrier layer; and forming a second adhesion layer over thesecond barrier layer. The silicon wafer substrate includes a pluralityof integrated circuits formed on a front side of the silicon wafersubstrate. The first adhesion layer includes at least one of: silicondioxide and silicon nitride. The second adhesion layer includes at leastone of: silver and tin.

In one example, the first adhesion layer has a thickness from 100nanometers to 400 nanometers. In one example, the second adhesion layerconsists of silver. In another example, the second adhesion layerconsists of tin.

In another example, an apparatus includes a package substrate, a lidattached to the package substrate, a plurality of integrated circuit diedisposed between the package substrate and the lid, and a plurality ofthermal conduction layers physically connecting the back side surface ofeach of the plurality of integrated circuit die to the lid. Each of theplurality of integrated circuit die are physically and electricallyconnected to the package substrate. Each of the plurality of integratedcircuit die includes a silicon substrate and a back side metallizationstructure. The silicon substrate has a front side surface and a backside surface opposite the front side surface. The silicon substrateincludes an integrated circuit device on front side surface. The backside metallization structure on the back side surface includes a firstadhesion layer, a first metal layer, a second metal layer, and a secondadhesion layer. The first adhesion layer is on the back side surface.The first adhesion layer includes at least one of: silicon nitride andsilicon dioxide. The first metal layer is over the first adhesion layer.The first metal layer includes titanium. The second metal layer is overthe first metal layer. The second metal layer includes nickel and,optionally, vanadium. The second adhesion layer is over the second metallayer. The second adhesion layer includes at least one of: silver, gold,and tin.

In one example, the plurality of thermal conduction layers includesiridium. In one example, the plurality of integrated circuit dieincludes at least one of: central processing unit cores, graphicsprocessing unit cores, and memory. In one example, the die of theplurality of integrated circuit die are not all the same.

Another example is a method of forming an apparatus including a packagesubstrate, a lid attached to the package substrate, and a plurality ofintegrated circuit die disposed between the package substrate and thelid, each of the plurality of integrated circuit die physically andelectrically connected to the package substrate. The method includesforming a metallization structure on a back side of a silicon wafersubstrate, in which the silicon wafer substrate includes a plurality ofintegrated circuits formed on a front side of the silicon wafersubstrate. Forming the metallization structure includes forming a firstadhesion layer including at least one of: silicon dioxide and siliconnitride on the back side of the silicon wafer substrate, forming a firstbarrier layer including titanium metal over the first adhesion layer,forming a second barrier layer including nickel and, optionally,vanadium over the first barrier layer, and forming a second adhesionlayer including at least one: of silver, gold, and tin over the secondbarrier layer. The method further includes cutting the silicon wafersubstrate into a plurality of die, each of the die including one of theplurality of integrated circuits, and attaching physically andelectrically at least two of the plurality of the die to the packagesubstrate. The method further includes applying a plurality of indiumpreforms by applying at least one of the plurality of preforms to thesecond adhesion layer for each of the integrated circuit die. The methodfurther includes attaching the lid to the package substrate andreflowing the plurality of indium preforms to physically bond the indiumto the second adhesion layer of each of the at least two of theplurality of die.

In another example, an apparatus includes a package substrate, a lidattached to the package substrate, a plurality of integrated circuit diedisposed between the package substrate and the lid, and a plurality ofthermal conduction layers physically connecting the back side surface ofeach of the plurality of integrated circuit die to the lid. Each of theplurality of integrated circuit die is physically and electricallyconnected to the package substrate. Each of the plurality of integratedcircuit die includes a silicon substrate and a back side metallizationstructure. The silicon substrate has a front side surface and a backside surface opposite the front side surface. The silicon substrateincludes an integrated circuit device on front side surface. The backside metallization structure on the back side surface includes a firstadhesion layer, a first metal layer, a second metal layer, and a secondadhesion layer. The first adhesion layer is on the back side surface.The first adhesion layer includes aluminum. The first metal layer isover the first adhesion layer. The first metal layer includes titanium.The second metal layer is over the first metal layer. The second metallayer includes nickel and, optionally, vanadium. The second adhesionlayer is over the second metal layer. The second adhesion layer includesat least one of: silver and tin.

In one example, the plurality of thermal conduction layers includesiridium. In one example, the plurality of integrated circuit dieincludes at least one of: central processing unit cores, graphicsprocessing unit cores, and memory. In one example, the die of theplurality of integrated circuit die are not all the same.

Another example is a method of forming an apparatus including a packagesubstrate, a lid attached to the package substrate, and a plurality ofintegrated circuit die disposed between the package substrate and thelid, each of the plurality of integrated circuit die physically andelectrically connected to the package substrate. The method includesforming a metallization structure on a back side of a silicon wafersubstrate, in which the silicon wafer substrate includes a plurality ofintegrated circuits formed on a front side of the silicon wafersubstrate. Forming the metallization structure includes forming a firstadhesion layer including aluminum on the back side of the silicon wafersubstrate, forming a first barrier layer including titanium metal overthe first adhesion layer, forming a second barrier layer includingnickel and, optionally, vanadium over the first barrier layer, andforming a second adhesion layer including at least one: of silver andtin over the second barrier layer. The method further includes cuttingthe silicon wafer substrate into a plurality of die, each of the dieincluding one of the plurality of integrated circuits, and attachingphysically and electrically at least two of the plurality of the die tothe package substrate. The method further includes applying a pluralityof indium preforms by applying at least one of the plurality of preformsto the second adhesion layer for each of the integrated circuit die. Themethod further includes attaching the lid to the package substrate andreflowing the plurality of indium preforms to physically bond the indiumto the second adhesion layer of each of the at least two of theplurality of die.

In another example, an apparatus includes a package substrate, a lidattached to the package substrate, a plurality of integrated circuit diedisposed between the package substrate and the lid, and a plurality ofthermal conduction layers physically connecting the back side surface ofeach of the plurality of integrated circuit die to the lid. Theplurality of thermal conduction layers includes indium. Each of theplurality of integrated circuit die is physically and electricallyconnected to the package substrate. Each of the plurality of integratedcircuit die includes a silicon substrate and a back side metallizationstructure. The silicon substrate has a front side surface and a backside surface opposite the front side surface. The silicon substrateincludes an integrated circuit device on front side surface. The backside metallization structure on the back side surface includes a firstmetal layer, a second metal layer, and an adhesion layer. The firstmetal layer is on the back side surface. The first metal layer includestitanium. The second metal layer is over the first metal layer. Thesecond metal layer includes nickel. The adhesion layer is over thesecond metal layer. The adhesion layer includes at least one of: silver,gold, and tin.

In one example, the second metal layer consists of nickel. In oneexample, the plurality of integrated circuit die includes at least oneof: central processing unit cores, graphics processing unit cores, andmemory. In one example, the die of the plurality of integrated circuitdie are not all the same.

Another example is a method of forming an apparatus including a packagesubstrate, a lid attached to the package substrate, and a plurality ofintegrated circuit die disposed between the package substrate and thelid, each of the plurality of integrated circuit die physically andelectrically connected to the package substrate. The method includesforming a metallization structure on a back side of a silicon wafersubstrate, in which the silicon wafer substrate includes a plurality ofintegrated circuits formed on a front side of the silicon wafersubstrate. Forming the metallization structure includes evaporating afirst metal layer including titanium onto the back side of the siliconwafer substrate, evaporating a second metal layer including nickel overthe first metal layer, and evaporating an adhesion layer including atleast one: of silver, gold, and tin over the second metal layer. Themethod further includes cutting the silicon wafer substrate into aplurality of die, each of the die including one of the plurality ofintegrated circuits, and attaching physically and electrically at leasttwo of the plurality of the die to the package substrate. The methodfurther includes applying a plurality of indium preforms by applying atleast one of the plurality of preforms to the second adhesion layer foreach of the integrated circuit die. The method further includesattaching the lid to the package substrate and reflowing the pluralityof indium preforms to physically bond the indium to the second adhesionlayer of each of the at least two of the plurality of die.

FIG. 1 is a schematic top view of a multi-chip package 10, according tosome embodiments of the disclosure. FIG. 1 shows the multi-chip package10 includes a package base 12 and a plurality of integrated circuit die14. The package base may be formed of ceramic, metal, and/or plastic,and includes electrical traces (not shown) to connect at least some ofthe integrated circuit die 14 to electrical connections (not shown)outside of the package, as is known in the art. In some embodiments, thepackage base may further include additional electrical traces (notshown) to connect at least some of the integrated circuit die 14 toother of the integrated circuit die.

The plurality of integrated circuit die 14 can be, for example, andwithout limitation, central processing units, graphics processing units,memory units, or input/output units, network processors, fieldprogrammable gate arrays, and programmable logic devices. In someembodiments, some of the plurality of integrated circuit die 14 caninclude combinations of any of the forgoing integrated circuits. Forease of illustration, the plurality of integrated circuit die 14 isshown as identical. However, it is understood that embodiments includemulti-chip package 10 in which the plurality of integrated circuit die14 are not all the same. For example, in some embodiments, some of theplurality of integrated circuit die 14 can include central processingunits, while others include memory units, and still others includeinput/output units. Many combinations are possible. In addition,although the plurality of integrated circuit die 14 in the multi-chippackage 10 is shown as including eight integrated circuit die 14, it isunderstood that embodiments include multi-chip packages 10 having as fewas two integrated circuit die 14 or as many as 100 integrated circuitdie 14.

FIG. 2 is a schematic side cross-sectional view of the multi-chippackage 10 of FIG. 1, according to some embodiments of the disclosure.As shown in FIG. 2, the multi-chip package 10 further includes a lid 16and a plurality of thermal conduction layers 18, one thermal conductionlayer 18 for each of the integrated circuit die 14. As further shown inFIG. 2, each of the integrated circuit die 14 includes a plurality ofsolder bumps 20 (three shown for each in FIG. 2). The lid 16 may be madeby stamping and formed of nickel plated copper. The thermal conductionlayers 18 may be formed of a material having a high degree of thermalconductivity and that will readily bond to metal surfaces. In someembodiments, the thermal conduction layer 18 can be indium. Indium canbond to well to some metals when reflowed at around 150° C., providedthat a flux is also employed, as is known in the art. The solder bumps20 can be formed of a material having a high degree of electricalconductivity and that will readily bond to metal surfaces when reflowed.Such materials are known in the art.

The lid 16 can be bonded to the package base 12 at the periphery of thepackage base 12, as shown in FIG. 2. The lid 16 may be bonded to thepackage base 12 by, for example, an adhesive, as is known in the art. Sodisposed, the lid 16 can protect the plurality of integrated circuit die14 from physical and environmental hazards. The solder bumps 20electrically connect the integrated circuit die 14 to the package base12. The thermal conduction layer 18 is disposed between the integratedcircuit die 14 and the lid 16. So disposed, the thermal conduction layeris able to provide a thermal path from the integrated circuit die 14 tothe lid 16. The lid 16 has a larger surface area than the integratedcircuit die 14 and may also be exposed to external convective aircurrents. Together, effects can make the lid 16 an effective heat sink.

In operation, each of the plurality of integrated circuit die 14 canproduce significant heat which must be dissipated to prevent detrimentaleffects, as described above. The heat can be conducted from theintegrated circuit die 14 through the thermal conduction layer 18 and tothe lid 16 where it is removed by external convective air currents.

FIG. 3 is a schematic side cross-sectional view of a portion of anintegrated circuit device wafer 22, according to some embodiments of thedisclosure. FIG. 3 shows the integrated circuit device wafer 22 includesa silicon wafer substrate 24 having a front side surface 26 and a backside surface 28 opposite the front side surface 26. The silicon wafersubstrate 34 also includes a plurality of integrated circuits 30 (shownin FIG. 4). The plurality of solder bumps 20 are formed on the front ofthe silicon wafer substrate 24, as descried above. The silicon wafersubstrate 26 can be diced along illustrated cut lines C to form theplurality of integrated circuit die 14, each with at one of theplurality of integrated circuits 30. The dicing can be by any number ofmethods known in the art including, for example, sawing or lasercutting.

FIG. 4 is a magnified schematic side cross-sectional view of a portionof the multi-chip package 10 of FIG. 2, according to some embodiments ofthe disclosure. As shown in FIG. 4, the integrated circuit die 14includes one of the integrated circuit 30 on the front surface 26 of thesilicon wafer substrate 24 and a back side metallization structure 32 onthe back side surface 28.

The back side metallization structure 32 is described in greater detailbelow in reference to FIGS. 5, 6, and 10 for various embodiments. Theback side metallization structure 32 provides a metal surface to whichthe thermal conduction layer 18 can readily bond. In addition, the backside metallization structure 32 can be well adhered to the silicon wafersubstrate 24 to provide a reliable thermal path from the integratedcircuit die 14 to the thermal conduction layer 18.

In FIG. 4, and in FIGS. 5-6 and 10 discussed below, the solder bumps 20which physically and electrically connect to the integrated circuit 32are omitted for clarity. In addition, for the purposes of clarity andease of illustration, the elements shown are not shown to scale.

FIG. 5 is a magnified schematic side cross-sectional view of a portionof the integrated circuit device wafer 22 of FIG. 4, according to someembodiments of the disclosure. In the embodiment shown in FIG. 5, theback side metallization structure 32 includes a first adhesion layer 34,a first metal layer 36, a second metal layer 38, and a second adhesionlayer 40. The first metal layer 34 and the second metal layer 36 can actas barrier layers to prevent the thermal conduction layer 18 frompassing through the back side metallization structure 34 to the siliconwafer substrate 24 where it could be detrimental to the integratedcircuit 30. In the embodiment of FIG. 5, the first adhesion layer 34 canbe silicon dioxide, silicon nitride, or a combination of the two, suchas, silicon oxynitride. In some embodiments, the first adhesion layer 34can be formed by chemical vapor deposition techniques, such as lowpressure chemical vapor deposition, or plasma enhanced chemical vapordeposition, as is known in the art. In some embodiments, the firstadhesion layer 34 can have a thickness from 100 nanometers to 400nanometers. If the first adhesion layer 34 is thinner than 100nanometers, it may not completely cover the surface features of the backside surface 28 of the silicon wafer substrate 24, leading to gaps inthe adhesion of the back side metallization structure 32 to the siliconwafer substrate 24. If the first adhesion layer 34 is thicker than 400nanometers, it may reduce the thermal conductivity through the back sidemetallization layer 34 without providing any corresponding benefit.

The first metal layer 36 can include titanium. In some embodiments, thefirst metal layer 36 consists of titanium. In some embodiments, thetitanium can be deposited by sputter deposition. In other embodiments,the titanium can be deposited by evaporative deposition. The techniquesof sputter deposition and evaporative deposition to deposit metals arewell known in the art.

The second metal layer 38 can include nickel and, optionally, vanadium.In some embodiments, the first metal layer 38 consists of nickel andvanadium. In some embodiments, the nickel and vanadium can be depositedby sputter deposition. Sputtering the vanadium along with the nickeldisrupts the natural ferromagnetic properties of the nickel, which couldotherwise interfere with the sputter deposition process. In otherembodiments, the first layer 38 consists of nickel. In some embodiments,the nickel can be deposited by evaporative deposition.

The second adhesion layer 40 can include silver, gold, or tin, orcombinations of any of the foregoing. In some embodiments, the secondadhesion layer 40 consists of silver. In other embodiments, the secondadhesion layer 40 consists of gold. In still other embodiments, thesecond adhesion layer 40 consists of tin.

FIG. 6 is a magnified schematic side cross-sectional view of a portionof the integrated circuit device wafer 22 of FIG. 4, according to someother embodiments of the disclosure. The embodiment of FIG. 6 issubstantially identical to the embodiment of FIG. 5, except that theback side metallization structure 32 is replaced by the back sidemetallization structure 34. In the embodiment shown in FIG. 6, the backside metallization structure 42 includes a first adhesion layer 44, afirst metal layer 46, a second metal layer 48, and a second adhesionlayer 50. The first metal layer 44 and the second metal layer 46 can actas barrier layers. In the embodiment of FIG. 6, the first adhesion layer44 can include aluminum, for example, aluminum metal and aluminumalloys. In some embodiments, the first adhesion layer 44 can consist ofaluminum metal. In some embodiments, the first adhesion layer 44 can beformed by sputter deposition or evaporative deposition, as is known inthe art. In some embodiments, the first adhesion layer 44 can have athickness from 100 nanometers to 400 nanometers.

The first metal layer 46 can include titanium. In some embodiments, thefirst metal layer 46 consists of titanium. In some embodiments, thetitanium can be deposited by sputter deposition. In other embodiments,the titanium can be deposited by evaporative deposition.

The second metal layer 48 can include nickel and, optionally, vanadium.In some embodiments, the second metal layer 48 consists of nickel andvanadium. In some embodiments, the nickel and vanadium can be depositedby sputter deposition. In other embodiments, the first layer 38 consistsof nickel. In some embodiments, the nickel can be deposited byevaporative deposition.

The second adhesion layer 50 can include silver, or tin, or combinationsof any of the foregoing. In some embodiments, the second adhesion layer50 consists of silver. In other embodiments, the second adhesion layer50 consists of tin.

FIG. 7 is a flowchart illustrating a method for forming themetallization structure 32 on a back side 26 of a silicon wafersubstrate 24, according to some embodiments of the disclosure. Themethod begins at step 100 by forming the first adhesion layer 34 ofsilicon dioxide or silicon nitride on the back side 28 of the siliconwafer substrate 24 at step 102. This may be done by chemical vapordeposition, such as low pressure chemical vapor deposition, or plasmaenhanced chemical vapor deposition. Next, at step 104, the first metallayer, or first barrier layer, 36 of titanium metal is formed over thefirst adhesion layer 34. This may be done by sputter deposition orevaporative deposition. Next, at step 106, the second metal layer, orsecond barrier layer, 38 including nickel and, optionally, vanadium isformed over the first barrier layer 36. This may be done by sputterdeposition or evaporative deposition. Next, at step 108, the secondadhesion layer 40 of silver, gold, or tin is formed over the secondbarrier layer 38. The second adhesion layer 40 may be formed by sputterdeposition or evaporative deposition to complete the metallizationstructure at step 110.

FIG. 8 is a flow chart illustrating a method for forming themetallization structure 42 on a back side 26 of a silicon wafersubstrate 24, according to some embodiments of the disclosure. Themethod begins at step 200 by forming the first adhesion layer 44 ofaluminum metal on the back side 28 of the silicon wafer substrate 24 atstep 202. This may be done by sputter deposition or evaporativedeposition. Next, at step 204, the first metal layer, or first barrierlayer, 46 of titanium metal is formed over the first adhesion layer 44.This may also be done by sputter deposition or evaporative deposition.Next, at step 206, the second metal layer, or second barrier layer, 48including nickel and, optionally, vanadium is formed over the firstbarrier layer 46. This may be done by sputter deposition or evaporativedeposition. Next, at step 208, the second adhesion layer 50 of silver ortin is formed over the second barrier layer 48. The second adhesionlayer 50 may be formed by sputter deposition or evaporative depositionto complete the metallization structure at step 210.

FIG. 9 is a flowchart illustrating a method for making an apparatus,such as the multi-chip package 10 including the package substrate 12,the lid 16 attached to the package substrate 12, and a plurality ofintegrated circuit die 14 from the integrated circuit device wafer 22attached to the package substrate 12, according to some embodiments ofthe disclosure. The method begins at step 300 by cutting the integratedcircuit device wafer 22 into individual integrated circuit die 14 atstep 302. This may be done by sawing or laser cutting, as is known inthe art. Next, at step 304, the individual integrated circuit die 14 arephysically attached and electrically connected to the package substrate12 by, for example, reflowing the solder bumps 20 to that they adhere toelectrical traces in the package substrate 12. Next, in step 306, atleast one indium preform is applied to each of the plurality ofintegrated circuit die 14. Depending on the embodiment, the indiumpreform is applied to the silver, gold, or tin of second adhesion layer40, or to the silver or tin second adhesion layer 50. Next, at step 308,the lid 16 is attached to the package substrate 12 by an adhesive, as isknown in the art. Next, at step 310, the indium preform 16 is reflowedto bond the indium to the silver, gold, or tin of second adhesion layer40 (or to the silver or tin second adhesion layer 50) and to the lid 16to complete the multi-chip package 10 at step 210.

FIG. 10 is a magnified schematic side cross-sectional view of a portionof the integrated circuit device wafer 22 of FIG. 4, according to someother embodiments of the disclosure. The embodiment of FIG. 10 issubstantially identical to the embodiments of FIGS. 5 and 6, except thatthe back side metallization structures 32 and 42 are replaced by theback side metallization structure 52. In the embodiment shown in FIG.10, the back side metallization structure 52 includes a first metallayer 54, a second metal layer 56, and an adhesion layer 58. The firstmetal layer 54 can act as both an adhesion layer and a barrier layer. Inthe embodiment of FIG. 10, the metal layer 54 can include titanium. Insome embodiments, the first metal layer 54 can consist of titaniummetal. In some embodiments, the first metal layer 54 can have athickness from 100 nanometers to 400 nanometers.

The second metal layer 56 can include nickel and can act as a barrierlayer. In some embodiments, the second metal layer 56 consists ofnickel. The adhesion layer 58 can include silver, gold, or tin, orcombinations of any of the foregoing. In some embodiments, the adhesionlayer 58 consists of silver. In other embodiments, the adhesion layer 58consists of gold. In other embodiments, the adhesion layer 58 consistsof tin.

FIG. 11 is a flowchart illustrating a method for making an apparatus,such as the multi-chip package 10 including the package substrate 12,the lid 16 attached to the package substrate 12, and a plurality ofintegrated circuit die 14 from the integrated circuit device wafer 22attached to the package substrate 12, according to some embodiments ofthe disclosure. The method begins at step 400 by forming the first metallayer 54 of titanium metal on the back side 28 of the silicon wafersubstrate 24 at step 402. This is done by evaporative deposition. Next,at step 404, the second metal layer 56 of nickel is formed over thefirst metal layer 54. This is also done by sputter deposition. Next, atstep 406, the adhesion layer 58 of silver, gold, or tin is formed overthe second metal layer 56. The adhesion layer 58 is formed byevaporative deposition to complete the metallization structure 52. Next,at step 408, the integrated circuit device wafer 22 is cut intoindividual integrated circuit die 14. This may be done by sawing orlaser cutting, as is known in the art. Next, at step 410, the individualintegrated circuit die 14 are physically attached and electricallyconnected to the package substrate 12 by, for example, reflowing thesolder bumps 20 to that they adhere to electrical traces in the packagesubstrate 12. Next, in step 412, at least one indium preform is appliedto each of the plurality of integrated circuit die 14. Depending on theembodiment, the indium preform is applied to the silver, gold, or tin ofadhesion layer 58. Next, at step 414, the lid 16 is attached to thepackage substrate 12 by an adhesive, as is known in the art. Next, atstep 416, the indium preform 16 is reflowed to bond the indium to thesilver, gold, or tin of the adhesion layer 52 and to the lid 16 tocomplete the multi-chip package 10 at step 420.

The above detailed description and the examples described therein havebeen presented for the purposes of illustration and description only andnot for limitation. For example, the operations described may be done inany suitable manner. It is therefore contemplated that the presentembodiments cover any and all modifications, variations or equivalentsthat fall within the scope of the basic underlying principles disclosedabove and claimed herein. Furthermore, while the above descriptiondescribes hardware in the form of a processor executing code, hardwarein the form of a state machine or dedicated logic capable of producingthe same effect, other structures are also contemplated.

What is claimed is:
 1. A method of forming a metallization structure ona back side of a silicon wafer substrate, the silicon wafer substrateincluding a plurality of integrated circuits formed on a front side ofthe silicon wafer substrate, the method comprising: forming a firstadhesion layer on the back side of the silicon wafer substrate, thefirst adhesion layer including at least one of: silicon dioxide andsilicon nitride; forming a first barrier layer including titanium metalover the first adhesion layer; forming a second barrier layer includingnickel over the first barrier layer; and forming a second adhesion layerover the second barrier layer, the second adhesion layer including atleast one of: silver, gold, and tin.
 2. The method of claim 1, whereinthe first adhesion layer is formed by chemical vapor deposition.
 3. Themethod of claim 1, wherein the first adhesion layer has a thickness from100 nanometers to 400 nanometers.
 4. The method of claim 1, wherein thefirst adhesion layer consists of silicon nitride.
 5. The method of claim1, wherein the second barrier layer further includes vanadium.
 6. Themethod of claim 1, wherein the second adhesion layer consists of silver.7. The method of claim 1, wherein the second adhesion layer consists oftin.
 8. A method of forming a metallization structure on a back side ofa silicon wafer substrate, the silicon wafer substrate including aplurality of integrated circuits formed on a front side of the siliconwafer substrate, the method comprising: forming a first adhesion layerincluding aluminum on the back side of the silicon wafer substrate;forming a first barrier layer including titanium metal over the firstadhesion layer; forming a second barrier layer including nickel over thefirst barrier layer; and forming a second adhesion layer over the secondbarrier layer, the second adhesion layer including at least one of:silver and tin.
 9. The method of claim 8, wherein the first adhesionlayer has a thickness from 100 nanometers to 400 nanometers.
 10. Themethod of claim 8, wherein the second barrier layer further includesvanadium.
 11. The method of claim 8, wherein the second adhesion layerconsists of silver.
 12. The method of claim 8, wherein the secondadhesion layer consists of tin.